634 
ZOSTERA 
each sta. with the cpl. on the same level with it forms a fir., the 
retinaculum representing the bract. 
Fertilisation occurs in a peculiar way, Z. being one of the water 
plants most completely modified from the ancestral land -plant type 
(see p. 158). The fir. is submerged like the rest of the plant. The 
pollen grains are long threads, of the same specific gravity as salt 
water, so that when they are discharged they float freely at any 
depth. The stigmas are very large, and thus have a good chance of 
catching some of the grains. The whole mechanism is very similar in 
principle to that of a wind-fertilised plant. The fruit is an achene. 
Delpino looks upon Z. as an Aroid, adapted to a submerged exist- 
ence. In winter it hibernates without any special modification. The 
plant is largely used for packing glass, stuffing cushions, &c., especially 
in Venice. [For further details see order, also p. 158 and Schenk’s 
Wassergewdckse. ] 
Zygadenus Michx. Liliaceae (1). 10 sp. N. Am., Siberia. 
Zygopetalum Hook, (inch Pescatorea Rchb. f.). Orchidaceae (20). 
20 sp. trop. Am., epiphytic. The base of the column forms a chin. 
Zygophyllaceae. Dicotyledons (Archichl. Geraniales). 22 gen. with 
140 sp. xero- or halo-phytes, trop. and subtrop. Most are woody 
perennials ; leaves opp., stip., usually hairy, fleshy or leathery. Firs, 
in cymes, regular, 5. K 5; C 5; A 5 + 5; obdiplostemonous and with 
ligular appendages ; G (5). Ovary 5-loc. with 1 or more pendulous 
ovules in each loc. Fruit usually a capsule. Seeds with or without 
endosperm. Guaiacum, Peganum, &c. furnish useful products. 
Chief genera : Zygophyllum, Guaiacum, Porlieria, Larrea, Peganum, 
Tribulus. Placed in Geraniales by Benth. -Hooker, in Terebinthinae 
by Warming. Closely related to Rutaceae. 
Zygophyllum Linn. Zygophyllaceae. 60 sp. Old World, deserts and 
steppes. Leaves and twigs fleshy. 
